1. Field of the Invention
The present invention relates to an encoding apparatus, an encoding method, a decoding apparatus, a decoding method, a recording apparatus, a recording method, a reproducing apparatus, and a reproducing method for processing a signal of for example audio data. The present invention also relates to a record medium for recording audio data and so forth.
2. Description of the Related Art
As a related art reference of a highly efficiently encoding method for an audio signal, for example, a transform encoding method is known. The transform encoding method is one example of a block-segmentation frequency band dividing method. In the transform encoding method, a time-base audio signal is segmented into blocks at intervals of a predetermined unit time period. The time-base signal of each block is converted into a frequency-base signal (namely, orthogonally transformed). Thus, the time-base signal is divided into a plurality of frequency bands. In each frequency band, blocks are encoded. As another related art reference, a sub band coding (SBC) method as an example of a non-block-segmentation frequency band dividing method is known. In the SBC method, a time-base audio signal is divided into a plurality of frequency bands and then encoded without segmenting the signal into blocks at intervals of a predetermined unit time period.
As another related art reference, a highly efficiently encoding method that is a combination of the band division encoding method and the SBC method is also known. In this highly efficiently encoding method, a signal of each sub band is orthogonally transformed into a frequency-base signal corresponding to the transform encoding method. The transformed signal is encoded in each sub band.
As an example of a band dividing filter used for the above-described sub band coding method, for example a QMF (Quadrature Mirror Filter) is known. The QMF is described in for example R. E. Crochiere xe2x80x9cDigital coding of speech in sub bandsxe2x80x9d Bell Syst.
Tech. J. Vol. 55. No. 8 (1976). An equal band width filter dividing method for a poly-phase quadrature filter and an apparatus thereof are described in ICASSP 83, BOSTON xe2x80x9cPolyphase Quadrature filtersxe2x80x94A new sub band coding techniquexe2x80x9d, Joseph H. Rothwiler.
As an example of the orthogonal transform method, an input audio signal is segmented into blocks at intervals of a predetermined unit time period (for each frame). Each block is transformed by for example a fast Fourier transforming (FFT) method, a discrete cosine transforming (DCT) method, or a modified DCT transforming (MDCT) method. As a result, a time-base signal is converted into a frequency-base signal. The MDCT is described in for example ICASSP 1987, xe2x80x9cSub band/Transform coding Using Filter Bank Designs Based on Time Domain Aliasing Cancellationxe2x80x9d, J. P. Princen and A. B. Bradley, Univ. of Surrey Royal Melbourne Inst. of Tech.
On the other hand, an encoding method that uses a frequency division width in consideration of the hearing characteristics of humans for quantizing each sub band frequency component is known. In other words, so-called critical bands of which their band widths are proportional to their frequencies have been widely used. With the critical bands, an audio signal may be divided into a plurality of sub bands (for example, 25 sub bands). According to such a sub band coding method, when data of each sub band is encoded, a predetermined number of bits is allocated for each sub band. Alternatively, an adaptive number of bits is allocated for each sub band. For example, when MDCT coefficient data generated by the MDCT process is encoded with the above-described bit allocating method, an adaptive number of bits is allocated to the MDCT coefficient data of each block of each sub band. With the allocated bits, each block is encoded.
An example of a related art reference of such a bit allocating method and an apparatus corresponding thereto is described as xe2x80x9ca method for allocating bits corresponding to the strength of a signal of each sub bandxe2x80x9d in IEEE Transactions of Acoustics, Speech, and Signal Processing, vol. ASSP-25, NO. 4, August (1977). As another related art reference, xe2x80x9ca method for fixedly allocating bits corresponding to a signal to noise ratio for each sub band using a masking of the sense of hearingxe2x80x9d is described in ICASP, 1980, xe2x80x9cThe critical band coderxe2x80x94digital encoding of the perceptual requirements of the auditory systemxe2x80x9d, M. A. Kransner MIT.
When each block is encoded for each sub band, each block is normalized and quantized for each sub band. Thus, each block is effectively encoded. This process is referred to as block floating process. When MDCT coefficient data generated by the MDCT process is encoded, the maximum value of the absolute values of the MDCT coefficients is obtained for each sub band.
Corresponding to the maximum value, the MDCT coefficient data is normalized and then quantized.
Thus, the MDCT coefficient data can be more effectively encoded. The normalizing process can be performed as follows. From a plurality of numbered values, a value used for the normalizing process is selected for each block using a predetermined calculating process. The number assigned to the selected value is used as normalization information. The plurality of values are numbered so that they increment by 2 dB of an audio level.
The above-described highly effectively encoded signal is decoded as follows. With reference to the bit allocation information, the normalization information, and so forth for each sub band, MDCT coefficient data is generated corresponding to a signal that has been highly efficiently encoded. Since a so-called inversely orthogonally transforming process is performed corresponding to the MDCT coefficient data, time-base data is generated. When the highly efficiently encoding process is performed, if the frequency band is divided into sub bands by a band dividing filter, the time-base data is combined using a sub band combining filter.
When numbered normalization information is changed by an adding process, a subtracting process, or the like, a reproduction level adjusting function, a filtering function, and so forth can be accomplished for a time-base signal of which a highly efficiently encoded data has been decoded. According to this method, since the reproduction level can be adjusted by a calculating process such as an adding process or a subtracting process, the structure of the apparatus becomes simple. In addition, since a decoding process, an encoding process, and so forth are not excessively required, the reproduction level can be adjusted without a deterioration of the signal quality. In addition, in this method, even if a highly efficiently encoded signal is changed, since the time period of the decoded signal does not vary, when numbered normalization information is changed, part of the signal generated by the decoding process can be changed.
In the reproduction level adjusting process and the filtering process that can be accomplished by changing normalization information of the highly efficiently encoded information, unless any special device is disposed, a predetermined function is performed at a designated time period. Thus, the functions are restricted. For example, in the reproduction level adjusting function, the same reproduction level is kept at a designated predetermined time period. On the other hand, in the filtering function, the same function is performed at a designated time period.
Therefore, an object of the present invention is to provide an encoding apparatus, an encoding method, a decoding apparatus, a decoding method, a recording apparatus, a recording method, a reproducing apparatus, and a reproducing method that accomplish various functions corresponding to a change of normalization information. Another object of the present invention is to provide a record medium for recording changed normalization information.
A first aspect of the present invention is an encoding apparatus for highly efficiently encoding an input digital signal, comprising a band dividing means for dividing the input digital signal into a plurality of frequency band components, an encoding means for block-segmenting a sequence of samples arranged in a time-base direction and/or a frequency-base direction of the input digital signal divided in the plurality of frequency band components and encoding each block, a normalization processing means for normalizing a signal component of each block encoded by the encoding means and generating normalization signal, a quantization coefficient calculating means for calculating quantization coefficients that represent a feature of the signal component of each block, a bit allocating means for deciding the number of allocated bits for each block corresponding to the quantization coefficients calculated by the quantization coefficient calculating means, a normalization information changing means for gradually changing the normalization information generated by the normalization processing means corresponding to a user""s operation on a time base, and an encoded data generating means for re-quantizing the signal component of each block corresponding to the normalization information changed by the normalization information changing means and the number of allocated bits allocated by the bit allocating means and generating encoded data corresponding to a predetermined format.
A second aspect of the present invention is a decoding apparatus for decoding a digital signal that has been highly efficiently encoded, comprising a normalization information changing means for changing normalization information contained in encoded data that is input corresponding to a user""s operation, a bit allocation decoding means for deallocating allocated bits corresponding to the normalization information changed by the normalization information changing means and to bit allocation information contained in the input encoded data, a plurality of decoding means for decoding an output signal deallocated by the bit allocation decoding means into a time-base sample sequence corresponding to block size information contained in the encoded data for each frequency band component, and a filtering means for combining signals of all the frequency band components that are output from the plurality of decoding means and generating a decoded signal of all the frequency band.
A third aspect of the present invention is a recording apparatus for highly efficiently encoding an input digital signal and recording the encoded signal to a record medium, comprising a band dividing means for dividing the input digital signal into a plurality of frequency band components, an encoding means for block-segmenting a sequence of samples arranged in a time-base direction and/or a frequency-base direction of the input digital signal divided in the plurality of frequency band components and encoding each block, a normalization processing means for normalizing a signal component of each block encoded by the encoding means and generating normalization signal, a quantization coefficient calculating means for calculating quantization coefficients that represent a feature of the signal component of each block, a bit allocating means for deciding the number of allocated bits for each block corresponding to the quantization coefficients calculated by the quantization coefficient calculating means, a normalization information changing means for gradually changing the normalization information generated by the normalization processing means corresponding to a user""s operation on a time base, an encoded data generating means for re-quantizing the signal component of each block corresponding to the normalization information changed by the normalization information changing means and the number of allocated bits allocated by the bit allocating means and generating encoded data corresponding to a predetermined format, and a recording means for recording encoded data generated by the encoded data generating means to the record medium.
A fourth aspect of the present invention is a reproducing apparatus for reproducing a digital signal that has been highly efficiently encoded from a record medium, comprising a reproducing means for reproducing the highly efficiently encoded digital signal from the record medium, a normalization information changing means for changing normalization information contained in encoded data that is input corresponding to a user""s operation, a bit allocation decoding means for deallocating allocated bits corresponding to the normalization information changed by the normalization information changing means and to bit allocation information contained in the digital signal reproduced by the reproducing means, a plurality of decoding means for decoding an output signal deallocated by the bit allocation decoding means into a time-base sample sequence corresponding to block size information contained in the encoded data for each frequency band component, and a filtering means for combining signals of all the frequency band components that are output from the plurality of decoding means and generating a decoded signal of all the frequency band.
A fifth aspect of the present invention is a record medium for recording encoded data generated by the steps of (a) dividing the input digital signal into a plurality of frequency band components, (b) block-segmenting a sequence of samples arranged in a time-base direction and/or a frequency-base direction of the input digital signal divided in the plurality of frequency band components and encoding each block, (c) normalizing a signal component of each block encoded at step (b) and generating normalization signal, (d) calculating quantization coefficients that represent a feature of the signal component of each block, (e) deciding the number of allocated bits for each block corresponding to the quantization coefficients calculated at step (d), (f) gradually changing the normalization information generated at step (c) corresponding to a user""s operation on a time base, and (g) re-quantizing the signal component of each block corresponding to the normalization information changed at step (f) and the number of allocated bits allocated at step (e) and generating encoded data corresponding to a predetermined format.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.